Progressive sensory hearing loss and/or balance disorders can be commonly due to perilymphatic fistulas. This is indicated by clinical and human temporal bone studies. The proposed investigations will be performed to evaluate the presence of health consequences of perilymphatic fistulas in humans and animals. These investigations are based on the findings of our preliminary studies. Human postmortem studies using a previously defined single blind clinical-temporal bone histopathologic experimental paradigm coupled with the prospective consecutive autopsy temporal bone histopathologic paradigm will allow a determination of the incidence of patency of the fissula ante fenestram, round window niche, posterior canal ampulla, and/or other communications between the perilymphatic space and the middle ear. The alterations of the membranous labyrinth associated with patencies, and the permeability and variations of permeability of the fissula and/or fissure will be studied. Animal studies will address both naturally occurring patencies of the fissula ante fenestram (in monkeys) and similarly placed but artificially produced fistulas (in cats, then monkeys). Evaluation of hearing changes will be performed using evoked response methods and of balance using standard vestibular test methods. In cats tracer methods will be developed which can be used in humans and animals to objectively determine the presence of a perilymph leak (fistula).